Scientific name: Orconectes rusticus
Common name(s): Rusty crayfish
Rusty crayfish is a Crustacean, just like lobsters, crabs and shrimp. But, the crayfish lives in freshwater. The others are generally found in saltwater.
Most people are familiar with creatures of the order Decapoda, more commonly known as crayfish, crawfish or crawdads. There are crayfish that are native to Minnesota, but the crayfish pictured here is not. It's a newcomer to the state of Minnesota, and it's known as the Rusty Crayfish. The Rusty Crayfish is native to areas in East Central United States.
Crayfish are found in all sorts of habitat, including wetlands, lakes, streams, rivers and even caves. The Rusty Crayfish is one of the least commonly encountered crayfish in Minnesota. It's found primarily in a few eastern and some northern streams, rivers and lakes. Like most crayfish, it lives among weeds and rocks on the substrate or layer of material beneath the water.
Crayfish tend to hide from people, so a good way to see them active is with a flashlight at night. The light shines on the crayfish so you can see them, but they can't see you behind the light so they don't scurry away as readily.
While they crawl along the bottom, Rusty Crayfish feed on both plants and animals. They are omnivores like us, but are considered scavengers because they are often found feeding on dead or dying fish and other aquatic animals (they actually prefer fresh meat). The Rusty Crayfish has blade-like mandibles (mouth parts) that can slice through plant material quite effectively.
As you might be able to tell, a crayfish can be dangerous to pick up because of their big claws or pincers. You have to be careful when handling them because they can pinch quite hard, and some have sharp points on the tips of their pincers that can pierce the skin.
You probably don't have to worry about being bitten, because their mouths are tucked up underneath their heads, more or less below their eyes. But nonetheless, be careful when you pick them up.
The Rusty Crayfish is one of the few animals found in the state of Minnesota that is considered an invader. What that means is that the rusty crayfish in not native to Minnesota. It was introduced from a population of crayfish outside of the state. This type of introduction can mean big problems if the animal being introduced outcompetes native animals that are found in similar habitats. This can lead to the elimination or decrease of native animal populations.
So far, this is not the case with the Rusty Crayfish in Minnesota. However, "rusties" have been documented as replacing native crayfish in Wisconsin. The problem with the "rusty" in Minnesota is that it is more aggressive, grows faster and reproduces faster than most native crayfish. For these reasons it is illegal to transport rusty crayfish from one waterbody to another in Minnesota.
The only real way to tell a rusty crayfish from others, is that they usually have a large rusty spot on each side of their bodies (see the area in the red circle in the photo at right). So if you find one, be careful, and leave it where you found it.
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The bug highlighted on this page was collected by MPCA's Water Quality Lab. This lab samples and analyzes water from around Minnesota.